The sign used is the one used to regulate traffic manually, as defined in Book I, Part 8 of the Interministerial Instruction on Road Signs and Signals: two-sided mobile post, model K10 (one per signaller).
Signallers on motorbikes may manually regulate traffic without a K10 sign as long as they are wearing an approved helmet and a high-visibility waistcoat as referred to in article R. 416-19 of the Highway Code. To do this, the signallers use the gestures required by the regulations to bring vehicles to a halt and put them back on the road.
They may also use pre-signed K2 barricades to indicate a temporary obstacle, on which the word “Race” will be written.
Where appropriate, a sign indicating the start of the race should be placed on top of the opening cars and a sign of the same type indicating the end of the race should be placed on top of the marshalling cars. The marshals in these vehicles may use megaphones.